Patent literature 1 discloses a hydraulic brake system including (a) a manually-operated hydraulic-pressure generating device, (b) a power-operated hydraulic-pressure generating device including a pump device and an accumulator, (c) a reservoir, (d) a common passage to which a plurality of brake cylinders are connected, (e) a pressure-increasing linear control valve provided between the common passage and the power-operated hydraulic-pressure generating device and a pressure-reducing linear control valve provided between the common passage and the reservoir, (f) an ON/OFF control valve provided between the common passage and the manually-operated hydraulic-pressure generating device, and (g) a hydraulic-pressure control device configured to control a hydraulic pressure in the common passage, by controlling the linear control valves and the ON/OFF control valves. In this hydraulic brake system, when a brake application is to be released, the pressure-reducing linear control valve is placed into its open state, before the ON/OFF control valve is switched from its closed state to its open state, so that the hydraulic pressure in each of the brake cylinders can be rapidly returned to the atmospheric pressure whereby a brake dragging can be satisfactorily prevented.
Patent literature 2 discloses a hydraulic brake system including (a) a manually-operated hydraulic-pressure generating device, (b) a power-operated hydraulic-pressure generating device, (c) a reservoir, (d) a common passage, (e) a pressure-increasing linear control valve provided between the common passage and the power-operated hydraulic-pressure generating device, (x) a plurality of individual pressure-holding valves each of which is provided between the common passage and a corresponding one of the brake cylinders, and (y) a plurality of individual pressure-reducing valves each of which is provided between the reservoir and a corresponding one of the brake cylinders, wherein at least one of the plurality of pressure-reducing valves is constituted by a linear control valve such that a hydraulic pressure in the common passage is controlled by controlling the at least one of the pressure-reducing valves constituted by the linear control valve. Since the hydraulic pressure in the common passage is controlled by utilizing the individual pressure-reducing valves, it is possible to reduce a required number of the electromagnetic valves.
Patent literature 3 discloses a hydraulic brake system including (a) a manually-operated hydraulic-pressure generating device, (b) a power-operated hydraulic-pressure generating device, (c) a reservoir, (d) a common passage, (p) a plurality of pressure-increasing individual linear control valves each of which is provided between the common passage and a corresponding one of the brake cylinders and each of which is disposed in parallel with the other of the pressure-increasing individual linear control valves, and (q) a plurality of pressure-reducing individual linear control valves each of which is provided between the reservoir and a corresponding one of the brake cylinders and each of which is disposed in parallel with the other of the pressure-reducing individual linear control valves. An electric current is supplied to at least one of the plurality of pressure-increasing individual linear control valves, by an amount that is determined based on a target hydraulic pressure and a flow rate of a corresponding at least one of the brake cylinders. Owing to the provision of the plurality of individual linear control valves, it is possible to increase a rate of flow of a working fluid into each of the brake cylinders and a rate of flow of the working fluid from each of the brake cylinders.
Patent literature 4 discloses a transmission in which a single linear valve is provided for a plurality of actuators. In this arrangement, a required number of the linear valves can be made smaller than an arrangement in which a linear valve is provided for each one of the actuators, so that the manufacturing cost can be reduced.